Studies of actual ichtyological biodiversity in the European Atlantic Ocean and estimation of changes in the relative abundance of fish species in catches off Arcachon, on the shelf and in the Bassin d'Arcachon, from 1727 to the present day are made. These show that some previously dominant species are now rare. Several disappeared to the south of the Bay of Biscay, such as the bottom‐living elasmobranchs with low reproduction rates(Echinorhinus brucus, Squatina squatina, Raja batis, R. brachyura, R. clavata, Dasyatis pastinaca, Myliobatis aquila, Galeorhinus galeus, Mustelus asterias), and teleostean fishesTrigla lyraandEutrigla gurnardus.Overfishing with most fishing gears, but especially bottom trawls is responsible for their reduction. An additional study was made on tropical species which were not recorded before 1950 to the north of Portugal. The species includeZenopsis conchifer, Cyttopsis roseus, Chaunaxspp.,Sphoeroides pacbygaster. Tarpon atlanticus, Seriola rivoliana, S. dumerili, S. carpenteri, Lichia amia, Pomatomus saltator, Aluterus monoceros, Pisodonophis semicinctus, Lamprogrammus niger.Northward extensions in the distribution in Euro‐Atlantic sea waters of tropical fish are compared with results obtained in other regions of the South French Atlantic continental shelf. Ichthyological observations support previous results: 68.3% of the new records were fished on upper slope (200 to600m); 19.5% from the continental shelf (0 to 200 m). Among them, some 66.7% of captures from the south of the Bay of Biscay; 12.2% of the new records were found in the middle slope (900 to 1100 m). These results confirm the following: (1) a northern extension of tropical fishes on the upper slope in the south of Portugal has increased since 1963, and while it began in 1969 on the continental shelf, only increased from 1981; (2) the rate of colonisation of new‐comers was low for several species. About 30 years have passed between the record ofZenopsis conchiferand that ofCyttopsis roseusfrom off Portugal and northwestern Ireland, but only 5 years in the case ofSphoeroides pacbygaster, and (3) the northward expansion is evident to 52°00'N for continental shelf species, to 55°30'N for upper slope, and to 60°00'N for mid‐slope species.